Switch-over system



Nov. 21, 195o M. N. YARDENY ET AL 2,531,187

SWITCH-OVER SYSTEM Filed April 25, 1948 3 Sheets-Sheet l Y INVENToRs MICHEL IV` YARDEN Y NOV- 21, 1950 M. N. YARDENY ET AL 2,531,187

SWITCH-OVER SYSTEM Filed April 23, 1948 I5 Sheets-Sheet 2 7m am RAD/0 /REC'E/VER/ INVENToRs MICHEL N. YARDENY BY ADOLPH RAZDUw/TZ M7; fr

A65/VT z i l Nov. 2l, T950 M. N. YARDENY ET AL SWITCH-OVER SYSTEM 3 Sheets-Sheet 5 Filed April 25, 1948 INVENTORS MICHEL N. YARnsNY BY ,wouw RAzDow/rz mmv ze www x Patented Nov. 21, 1950 2,531,187 SWITGH-OVER SYSTEM Michel N. Yardeny and Adolph Razdowit'z', Nett7V York, N. Y.; said Razdowitzassigno to said Yarden-y Application April 23, 1948, Serial No. 22,863

19 Claims.

The present invention'relates to remote control systems for selectively connecting a plurality oi' loads to a control circuit over a trans-l mission channel, a system of this general description having been disclosed in the copending United States patent application of Michel N. Yardeny and Robert Bernas, Ser. No. 5,276, filed January 30, 1948, now abandoned. in that system, a transmission channel is used to operate a plurality of loads, such as the various controls of a radio receiver located at a remote station, from a control station, the transmission channel serving both as a path for the receiver output and as means for transmitting signals to select and operate the various controls. further disclosed in our said co-pending application, the positioning of the various loads can be effected by connecting a pair of potentiometers across the control end and the remote end of the transmission channel, respectively, a loadoperating motor at the remote station determining the position of the second potentiometer and being energized as long as the voltages applied to the transmission channel by the two potentiometers differ.

An object of the present invention is to provide means for selectively operating a plurality of loads in a remote control system particularly, though not exclusively, of the type described in our aforesaid co-pending application.

Another object of the invention is to provide simple and dependable means for selectively connecting one of several loads to the remote end of a control channel.

A further object is to provide, in a remote control system comprising a transmission line adapted to transmit D.C. voltages, means for selective load switching utilizing D.C. voltages of one polarity only while reserving the D.C. voltages of opposite polarity for other control operations, such as the actuation of the respective load selected.

Stated briefly, a now preferred embodiment of the invention resides in a remote control system comprising a transmission line interconnecting a control station and a remote station, a voltage source at the control station operable to apply to the line a D.C. pulse of selected mag-- nitude, the internal impedance of said source being low compared with the impedance terminating the line at the remote end whereby the D.C. pulse will be transmitted to the remote end without substantial attenuation, and a D.C. responsive selector circuit at the remote station adapted to actuate one of several switching elements, according to the magnitude of the pulse received, and to maintain such switching element actuated after the pulse has subsided.

Preferably, the selector circuit is designed so that each new switching pulse received at the remote end of the lineV restores the previously selected switching element to its initial position before resulting in the actuation of the particular switching element corresponding to the magnitude of the new pulse. The invention also provides certain safeguards to prevent false operation and means designed to enhance the selectivity of the system, in order to render the operation virtually fool proof and to reduce the range of potentials required for carrying out any given number of switching operations.

The above and other features and objects of the invention will become more apparent from the following description, taken in conjunction with the accompanying drawing in which:

Fig. l is a typical circuit diagram of a control station according to the invention;

Fig. 2 is a typical circuit diagram of a remote station according to the invention;

Fig. 3 illustrates a timer circuit adapted to be used in combination with the arrangement of Fig. 1;

Fig. 4 illustrates a biasing circuit for the selector tubes of Fig. 2; and

Fig. 5 is a partial modication of the biasing circuit of Fig. 4.

Referring now to the drawing in detail, there is shown a control station (Fig. 1) and a remote station (Fig. 2) interconnected by suitable transmission means illustrated as a two-wire transmission line comprising conductors I and 2. The remote station is shown to comprise a radio receiver 3 having an audio output indicated at 4, a power supply shown as a battery 5 and a plurality of controls including a tuning control B, a volume control 'I and a band switch 8. These three controls are driven by respective motors 9, Iii, and II responsive to motor controls I2, I3, and I4, respectively, the latter being selectively connectable to the line I, 2 in a inanner subsequently to be described. The shafts:

of motors 9, Iii, and II also entrain the pointers of respective potentiometers I5, IE and I'I.

The actuating elements for the respective receiver controls are represented, at the control station, by knobs I9, I9 and 29 determining the setting of associated potentiometers 2I, 22 and 23, respectively. Each of these knobs is connected by way of a linkage 24, 25, 2E with an associated switch 21, 28, 29 which will close momentarily when the respective knob is being displaced; linkages 24, 25 and 26 may each be a conventional switching device which will auto-v matically restore the associated switch 21, 28,

29 to open position when the respective knob I8,

I9, 20 is released, A novel switching device par-I ticularly suitable for this purpose is disclosed in the co-pending application of Michel N.

v Yardeny and Robert Bernas, Ser. No. 17,883,

led March 30, 1948. In addition, there is pro- 3 vided an On switch 39 and an Off switch 3| each of which, in the simplied embodiment of the invention shown in Fig. l, may be a manually operated push button.

The switches 21 through 3| control a group of ve relays, generally indicated at 32, which include an On relay A, a tuning relay B, a volume relay C, a band switch relay D and an OIT relay E. Each of these relays is provided with two windings one of which is connectable in series with a battery 33 by the actuation of a respective switch These relays are arranged so that energization of any one of them will close a locking circuit which includes a back contact of each of the ther relays, whereby the continued energization of more than one relay will be impossible. The several armatures of relays A, B etc. are indicated at ai, a2, bl, b2 and so forth.

The locking circuit for the relays 32 includes a battery 34 connected to a conductor 35 and the primary of a transformer 36, the secondary of this transformer being connected in the grid circuit of a vacuum tube 31 shown as a tetrode. The load circuit of the tube 31 includes a relay 38 in series with a battery 39 and shunted by a condenser 43. The armature of relay 38 is connected to wire 2 by way of a conductor 4|, the latter also serving to connect the grid of a thyratron tube 42 to the wire 2.

Tube 42 is energizable from a source of alterz.

nating current 43 connected in series with a relay 44 which is shunted by a condenser 45. A conductor 46 connects the cathode of the thyratron 42 to the wire whereby the input circuit of the thyratron is connected across the transmission line 2. Thyratron 42 is biased or designed so that it will become conductive whenever the potential of conductor 4| exceeds a given positive value relative to conductor 46. The armature of relay 44 normally connects battery 33 to conductors 41 and 48 which, together with a bus conductor 49, form part of the energizing circuit for relays 32.

Line wire is also connected to the neutral terminal of a voltage divider having a negative terminal 5| and four positive terminals 52, 53, 54, and 55, the potentials for these terminals being obtained :from batteries 56 and 51, respectively. Preferably, the potential of terminal 5| is of the same order though opposite polarity asthat of terminal 55. Terminal 5| is connected by conductor 58 to the front contact of armature a2; the negative terminals 52 through 55 aresimilarly connected by conductors 59, 60, 6| and 62 to the front contact of armatures b3, c3, d3 and e3, respectively. A conductor 63 connects armature e3 to the front contact of relay 38.

Abattery S4 has its positive terminal connected to a bus conductor 65 for potentiometers 2|, 22 and 23 and has its negative terminal connected to armature d5 by a conductor 66. Between the conductors 65 and 46 there is inserted a resistor 61 having one terminal connected to armature d6 by way of a conductor 68, its other terminal being connected to a set of unbalance indicators 69, 18, 1| shown here schematically as lamps. Indicators 69, and 1| are connected by conductors 12, 13 and 14 to the front contacts of armatures o6, c6 and d6, respectively. The pointers of potentiometers |8, I9 and 20 are connected to the front contacts of armatures b4, c4 and d4 by conductors 15, 16 and 11, respectively. The remaining terminals of these potentiometers are connected to the front contacts rfa f ratrons |22, |23 and |24.

of armatures b5, c5 and d5 by conductors 18, 'I9 and 80, respectively.

Connected across the line 2 in a non-galvanic manner, as by way of two condensers 8|, 82, is a loudspeaker or other` reproducing device 83 responsive to alternating currents arriving over the line. A suitable iilter, shown here as an audio frequency choke 84 in series with wire and a condenser 85 shunted across the line, prevents these alternating currents from reaching the control circuit just described.

Referring now again to Fig. 2, there is shown a similar line-terminating filter consisting of a choke 85 in series with wire and a shunt condenser 81. Connected across the line ahead of the filter 86, 81 is the secondary of a transformer 88 whose primary forms part of the audio output circuit 4 of receiver 3. The provision of a condenser 89 in series with this secondary is necessary in order to prevent a virtual sh0rtcuiting of the line for direct current.

Connected permanently across the line l, 2, in series with a resistor 98 Whose magnitude should be large compared with that of voltage divider 50 (Fig. l), are a pair of parallel voltage dividers 9|, 92 each in series with a respective rectifier 93, 94. Rectiiiers 93 and 94 are oppositely poled. A portion of voltage divider 92 is connected between the cathode and the auxiliary electrode of a cold-cathode tube 95, by means of conductors 96 and 91; and a portion of voltage divider 9| is connected between the cathode and the auxiliary electrode of a cold-cathode tube 93, by means of conductors 91 and 99 and the left-hand armature of a relay |90.

The energizing circuit oi relay |66 includes a battery |E|| and leads over the armature and front contact or a relay |02 in series with the anode of tube 98, a similar relay |93 being in series with the anode of tube 95. Relays |62 and |93 are shunted by condensers |64 and |65, respectively. A source of alternating current |65 is connected across the main gap of tube by means oi" conductors |61, |38, 91 and across the main gap of tube 93 by means oi conductors |61, |68 and the left-hand armature of relay |06.

Source |25 is also connected across the primary of a transformer |39 whose secondary has one terminal connected to a conductor il@ and the other to the center` right-hand armature ol' relay |60. Raw rectified current from transformer |69 is fed to the vbus bar l! of motor controls i2, |3 and I4 by oi' a rectifier i |2 shunted by a condenser H3. Conductor HS also connects with a bus conductor H4 of a set of relays generally indicated at ||5, comprising the relays F, G, H, I and J. Each of the relays ||5 is shunted by a respective condenser H6, iii, H3, H9 and |26; the holding circuit of these relays includes a rectier |84 inserted in the conductor l |9.

Connected across the line i, 2 is further the input circuit of a thyratron 2| or the screen grid type, its cathode being connected to wire as are the cathodes or" three further. similar thy- The grids of thyratrons |22, |23 and |24 are connected, over the usual current limiting resistors, to terminals |25, |26 and |21, respectively, of a voltage divider |28 associated with a battery |29 whoseY positive terminal is connected to wire l over a very large resistor |30. The function of resistor |36 is to maintain the control grids of tubes |22, |23 and |24 at the correct bias potentials preparatory to the commencement of the switching operations described hereinafter. A bias potential is also applied to the screen grid of tube I2I by means of a battery |3I.

The anode of tube I2I is connected to the wind ings. of relays I and J in parallel by a conductor |32, the anodes or plates of tubes |22, |23 and|24 being similarly connected to the windings of relays F, G and H, respectively, by means of respective conductors |33, |34 and |35. A resistor |36, in series with line Wire I, has one terminal connected to armature zI by a conductor |31 and the other to armature i3 by a conductor |38, the latter terminal being also connected to the bus conductor |39 of potentiometers I5, I6 and I1. The pointers ol these potentiometers are connected by conductors |40, I4I, |42 to the front contacts of armatures f4, g4 and h4, respectively, while the remaining potentiometer terminals are connected by conductors |43, |44 and |45 to the front contacts of armatures f3, g3 and h3, respectively. Conductors |46, |41 and |48 connect motor controls I2, I3 and I4 to the front contacts of armatures f2, g2 and h2, respectively. A bate tery |49 has its positive terminal connected to bus conductor |39 and its negative terminal to the armature gid. Relay J, which may be slightly slow-operating, has armatures y' 5 and :i2 connected to wire 2, the front contact of armature i2 being connected to the positive terminal of battery .|29 by conductor |50.

The operation of the control circuit at the local station (Fig. l) is as follows:

Whenever one of the switches 21 through 3| is actuated, it connects battery 33 in series with the left-hand winding of the associated relay 32 which locks over its right-hand winding, sending a currentimpulse through the primary of transformer 36. This impulse is applied to the grid circuit of tube 31 with such a polarity as to render this tube momentarily conductive, energizing relay 38 which closes its front contact and conn nects wire 2 to a terminal of voltage divider 50 over a front contact of the operated relay 32. This pulse will be negative if the switch actuated was the On switch 30 (relay A operated) and will be positive in .all other instances. The duration of the pulse will be determined by the time relay 38 remains energized, dependent in turn on the value of condenser 40, and should be suflicient to permit the full potential of the selected divider terminal to be developed at the far end of the transmission line.

After the relay 39 releases, its armature falls back and, if the operated relay 32 is one of the switching-device-actuated relays B, C and D, connects Wire 2 over a front contact of such relay to the wiper of a respective potentiometer 2|, 22 or23. It should be noted that, in the exemplification illustrated, this latter operation will drive conductor 2 negative with respect to conductor I, but to a less extent than when an On pulse is applied to the line; hence there will be no interference between the negative control -voltages from the potentiometers, on the one hand, and either the negative On lpulse or the positive OIT or switching pulses, on the other.

When the highly negative On pulse arrives at the remote station (Fig. 2) after a period of inactivity, it will be of such a polarity as to pass the rectifier 93 and to set up a voltage difference across the exciting gap of tube 98 suicient to ionize theY latter, resulting, in turn, in the ener-gization of relay |02 which loses its front contact and operates relay |00. Relay locks over itsA inner right-hand front contact and armature and" over the armature and back `contactof relay |03,

at the same time removing the power from the main gap of tube 98 at the back-contact of its left-hand armature. Relay |00 also connects power to receiver 3 at its outer right-hand armature and front contact, and further connects the secondary of transformer |09 to wire I and, hence, to the cathodes of tubes I2I through |24 at its center right-hand armature and front contact.

If, now', a positive switching pulse is received, tube I2I as well as one or more of the progressively biased thyratrons |22, |23 and |24 will be momentarily ionized, depending on the magnitude of the pulse. The ionization of tube I2I energizes relay I and, immediately thereafter, relay J which opens the energizing circuit of relay I, causing it to release after an interval which is short compared with the duration of the pulse received. During the brief period of its operation, relay I at the back contact of its armaturev opens the holding circuit of any relay-F, G, H that may have been operated. Since one or more thyratrons |22, |23, |24 are conducting at this time, one or more relays F, G, I-I will-be energized but only the one corresponding to the tube with the highest bias will lock after relayV I releases. After the pulse has subsided, all the relays yI I5 except the one that has locked will be unoperated, their de-energization making it possible for the operated relay to connect a particular motor control I2, I3, I4 across the resistor |39 and the associatedpotentiometer I5, I6, I1 across the line I, 2.

The potential applied to conductor 2 by the selected potentiometer I5, IB or I1 Will be of the same polarity as that of a respective control potentiometer 2|, 22 or 23 simultaneously connected across the line by a particular relay 32, although not necessarily of the same magnitude; If the two potentials differ, the line will be unbalanced and current will flow through resistor 61 (Fig. l), lighting one of the unbalance indicators 69, 10, 1I. In practice, it will generally be necessary to amplify the voltage drop across resistor 61. Current will also ow through resistor |36 (Fig. 2), causing the respective motor control I2, I3 or I4 to respond and to energize the associated motor 9, I0 or II in such a sense as to decrease this potential difference; when the line is again in balance, the motor stops.

When an Off pulse is received, this pulse will pass through rectier 94 and voltage. divider 92 and will place a voltage difference across the exciting gap of tube 95 which ionizes, energizing relay |03 and breaking the holding circuit of relay |00 at the back contact and armature of relay I03. Power is disconnected from the receiver 3 and from the cathodes of thyratrons I2I through |24. The release of relay |00 again connects the generator |06 across the main gap of tube 98, placing this tube in readiness to respond to the next On pulse.

Considering the operation of the system in greater detail, we shall assume that the operator at the local station (Fig. 1) has depressed the On switch 30 for an instant, the remote station being in the idle condition following the reception of an OIT signal. Battery 33, back contact and armature of relay 44, conductor 48, switch 30, left-hand winding of relay A, conductor 49; and locks: Battery 34, secondary of transformer 36, armatures and back contacts eI, dI, cI and bI in series, right-handl winding of relay A, front contact and armature aI,v conductor 35. Relay 38 energizes and con-'f Relay A energlzes:

|., conductor 58, front contact and armature a2, backcontacts and armatures b3, c3, d3, and e3 in series, conductor 63, front contact and armature of relay 38, conductor 4I. Tube 98 ionizes, causing relays |00 and |02 to be energized. Power is connected to receiver 3 and the output of this receiver, as determined by the setting of the controls 6, l and 8, will be transmitted to the loudspeaker 83 overtransformer 38. and line. I, 2

Assume, now, that the operator desires to switch, to a different frequency band, actuating the knob for that purpose. Switch 29 is Closed momentarily, energizing relay D: Battery 3,3,k

back contact andv armature `of relay 44, conductor 4l, switch .-29, left-hand winding of relay D. Relay D releases relay `A by .Opening the holding circuit thereof at the back contact o f its arma ture dl, then locks.: Battery 34, secondary of transformer '36, armature andy back contact eI, right-hand winding of relay D, front contact and armature .rl-2, back contacts and armatures e2, b2, `all -in series, conductor 35. Relay 38 ener.- gizes momentarily and connects the positive potential'of terminal l54 to wire :2: Terminal 54, conductor BI, front contact and armature d3, back contact and armature e3, conductor 6:3', front contact and armature of relay 38, conductor M.

At the remote station, the positive -pulse 'lires thyratron lf2-I, relay I energizes: .Cathode `of tube I2I, front contact and .center armature of relay |00, secondary of transformer |09, conductor IIU, conductor ||4 back contact and armature 71|, conductor |32, plate of tube I2 I relay J operates in parallel with relay I, releases relay I and lat i2 Vconnects wire 2 lto conductor |58. The high 4resistor |30 is now connected across the line but is of such magnitude thatI the level ofthe pulse will not decrease appreciably. This pulse is now `applied to the inputs of thyr,atrgirrs |22, |23 and |24 in .oppositiony t0 lthe bias voltages developed Aacross the voltage divider 12B, Since the pulse has been ,obtained from the highly positive terminal 54 of voltage divider 5g, its magnitude will be suiicient to ionize all three thyratrons I 22, |23 and |24. Relays VF, G .and H energize: Wire I', front contact and .center armature offrelay IDG, secondary of transformer |09, conductor III), conductor H4, windings of relays F, G and H -i-n parallel, conductors |33, |34 and v|35, respectively. Relay alone, locks; Wire I, conductor i3?, armature and'back con.- tat isi, larmature and iront contact hl, .60nduc-tor II and at h2, h3-and h4 prepares the `circuits ifor connecting band switch kmotor control I44 and potentiometer I1 to the line.

At thel control station, the -posi-tivenpulse applied to .the line 2 has also iired the thyratron 42 whose exciting potential should :be-not nigher than the lowest positive pulse used the system, i. e. the potential of terminal 52. Thyratron 42 energizes relay 44 .which opens its armature,

thereby preventing for the time lbeing the com@ tion Qf a dime-rent relay 32. 'I his is necessary in order to lforestal-l `false `operation such as might occur if a new :sw-itching operation were irri-,tiated before lthe previous pulse had decayed suiiiciently essersi. relay 4.4 may be made slightly slow-releasing.

motor control I4, conductcr M8, front Contact and.armeturev h2., Vvback Contact and armature i3.,-

conductor |38. At thesame time, battery |149 is connected across potentiometer I`I; conductor- |39', potentiometer I1,- conductor |45, front contact and armature h3, back contact and armature 94. Also, the Wiper of potentiometer I'I is connected to wire. 2;' Conductor" |42,- front contact and armature h4, back contact and armature d5'. Meanwhile, at the control station, the end of the pulse has been marked by the release of relay 38 which now connects the wiper of band switch control 23 to Wire 2: Conductor 71, front contact and armature d4, back contact and a1'- ma-ture of relay 38, conductor 4|. energization of relay D had connected the negative terminal of battery 64 to potentiometer 23: Conductor 66, front contact and armature d5, conductor '18. At the same time, the unbalance indicator `I| had been connected across resistor B'I: Conductor 14, iront contact and armature-d6,

\ conductor 68.

clockwise direction. Lamp 1| will be lit until the two voltages are equal, at which time the motor II will cease to rotate. In similar manner the potentiometers I5 and I6 may be brought into a desired position, relay H being released at z'I when the next switching pulse is transmitted.

When .the Oi signal is given, relay E operates and locks, tube 95. res and relay releases as previously described. While this is a positive pulse, tubes I2| through |24 will be energized only for an instant since power will be removed therefrom as soon as the armatures of relay |00 are restored to unattracted position. The receiver 3V and the selector` circuit of Fig. 2f now remains quiescent until the next On pulse is sent over the line.

Where the On pulse is used to connect not only the plates but also the heaters (not shown) of tubes |2I-I24 to their respective sources of current, false operation may result from the transmission of a switching pulse before these tubes have had time to Warm up sufficiently. Another source of error resides in the possibility that a control knob be displaced, either at thev local or at the distant station, while-the two that the operator desires to leave this particu-lar control in its position and the -maladjustment may remain unnoticed fora prolonged period.

Assume, for example, that the band switch knob 20, Fig. 1, had been brought into .the pcsi.-`

tion shown while the remote station was quies-L- cent. After the On switch has been depressed, `the operator. being satisfied with the positioning of that knob and believing the. receiver to be ad justed accordingly, proceeds with the manipulation of tuning control I8 and volume control I9, unaware that he is receiving an unwanted band. of frequencies. Since no band switch pulse is- Earlier, the

- Wiper ever transmitted, potentiometer |I will remain by the provision of a timer circuit as shown in Fig. 3. As indicated, the circuit of Fig. 3 replaces that part of Vthe control circuit which is shown between the lines X-X and Y-Y in Fig. 1, includ- 'ing On switch 30, 01T switch 3| and conductor This timer is provided with two banks of from an A.C. motor |55 which is energized by a source of alternating current |56. Contact bank |5| comprises the arcs or segments |5|a, |5|b,

arcs r segments |52a, |5217, |52c, |52d and |52e.

A manually operable On-Off switch |51 has its On" contact connected to arc or segment |5|a and its Off contact to arcor segment |5|c; segments |5|b and |5|d are connected to a conductor |58, as are the movable arm of switch.

|51 and one terminal of motor |55. Conductor |59 connects motor |55 and source |56 in series to the wiper |53. There may further be provided a synchronization circuit generally indicated at |60.

A conductor |6| connects wiper 54 to its power source (battery 33). Conductors |62, |63 and |64 connect segments |52a, |52b and |52c to the -On"'relay A, the band switch relay D vand the tuning relay B', respectively; conductors' |63 and |64 also connect relays D and B to their respective actuating switches 29 and 21. The volume relay C is through-connected to its actuating switch 28 by a conductor |65 having no connection with the timer. Conductor |66 connects the winding of relay 44 in series with generator 43 and tube 42, its armature connecting conductor 41 to arc I52d.

The Off relay E is connected to segment 52e over a conductor |61.

The operation of the timer circuit is as follows:

Since the energizing circuit of motor |55 is open at switch |51, nothing will happen until the switch is brought into its On position where it will be left as long as communication with the distant station is desired. Motor |55 now energizes: Conductor |58, switch |51, segment |5|a, wiper |53, conductor |59, generator |56. Wiper |53 begins to travel in a counterclockwise direction and, on reaching segment |5|b, closes the following circuit: Conductor |58, segment |5|b, wiper |53, conductor |59, generator |56, motor |55. The

.motor remains energized until the wiper reaches segment |5|c.

|54 is displaced synchronously with wiper |53. As it reaches segment |52a, relay A is energized, sending an On pulse over the line: Battery 33, conductor I6 I, Wiper |54, segment I52a, conductor |62, left-hand winding of relay A, conductor 49. After an interval suicient to place the remote station in full operative condition, wiper |54 engages segment |52b and a band switch synchronizing pulse is transmitted by the energization of relay D: Battery 33, con- .ductor |6I, wiper |54, segment |52b, conductor |63, left-hand winding of relay D, conductor 49. Similarly, a tuning control synchronizing. pulse l 10 is subsequently sent out by the energization of relay B over a circuit which includes segment |52c and conductor |64.

When the timing motor stops, wiper |54 is in contact with arc |5211. In this position, conductor 41 is connected to battery 33 via the armature and back Contact of relay 44, segment |52d, wiper |54 and conductor 16E, thus placing the relays B, C and D under the control of their respective clutch-operated switches 21, 28 and 29 for the first time. False operation is again prevented by the energization of relay 44 when a positive pulse appears across the transmission line 2.

When the switch` |51 is thrown into 01T position, motor |58 again energizes: Conductor |58, switch |51, segment |5|c, wiper |53, conductor |59, generator |56. Wiper |53 continues to advance and maintains motor |55 energized, over segment |5|d, untii it comes to rest in the position illustrated. As the wiper |56 passes segment |52e, relay E is energized: Battery 33, conductor |6I, wiper |54, segment 252e, conductor |61. Thus an Off pulse is sent to the selector circuit at the remote station.

The transmission of the band switch and tuning control synchronization pulses insures that the settings of the respective potentiometers at the remote station correspond to the settings of those at the control station when the system is ready for manual control. It will, of course, be understood that a receiver or other apparatus to be operated in the manner described may have a larger number of controls than herein illus- 'trated and that quite a few of these controls may be of such'nature that the operator cannot readily ascertain the absence of synchronization. In such cases the transmission of three, four or more synchronizingpulses by the timer may be required before the system is placed in condition for manual operation.

The synchronization circuit comprises a manual switch 68 connected to generator |56 over a conductor |69, and a relay |10 shunted by a condenser |1| and connected to segment |5|c by way of a rectier |12. The provision of this circuit enables the operator to check the synchronization of the controls referred to when the timer is in its operative position (wiper |53 on arc |5|c, wiper |54 on arc |52d). When the switch |68 is momentarily depressed, rectified current from generator |56 ows through relay |10 by way of conductor |59, wiper |56, segment |5|c and conductor |68, relay |10 locking over its lower armature. .At its upper armature relay |10 connects motor |55 to segment |5|a, causing the wipers to advance just as if switch E51 had been placed in its Off position. When the wiper |53 leaves segment |5|c, relay |10 releases. When the wiper nally reaches segment |5|a, it does not stop in the position shown in the drawing because switch |51 is still in its On position. Thus the timer steps round until it returns to'its operative position, having thus completed a full cycle during which, successively, an Off pulse, an On pulse and the synchronizing pulses for the band switch and tuning control were sent over the line. Proper synchronization has thereby been insured and the transmission continues.

A. further refinement, designed to eliminate errors due to variations in the ring point of the thyratrons, is illustrated. in. A. and 5. It is known that external factors, such as changes in the ambient temperature and iiuctuations in the power supply, may critically aect the biasing woltage .at which -a gaseiilledtube, for-:example 'a .thyratron, becomes ionized. Such instability would, of course, necessitateswideseparation of @the various pulse levels which, in turn, would lead tovery .high signaling voltages if the num- -ber of functions to be controlled is large.

The Vbiasing arrangement in Fig. -4 is-fadapted to enhance the stability of ithe firing .pointfoiatevatron, e. g. thyratron r2.3., nig.- 2, so as to -render the same responsive lton-switching pulses resistor of avacuumntube |f11 whose-gridA is .con-

nected to terminal .|26 by way of a resistor Hi8. At |19 .there is shown a battery delivering .anode voltage .to the :plate of tube-.111 by way of :a -revsistor |89. Therinputiresistor |81 corresponds to that portion fof .voltage-.divider |28 .acrosswhich 'fthe bias'voltage vfor thyratron-.fl developed.

The provision -o'f lbattery |114 and Avoltage .di- -vider |15, |16 biases the 'screen grid of the thyratron so that the iiring potential zis` increased beyond that of the pulse to which the thyratron should respond. Also,:.tube ;|'1-1:isbiased to cutoff :by the potential lnormally existing :on terminal X.|f2f'i. If, however, .a 4positive :pulse of @the --desired vmagnitude is received, Vtube -|-J1 becomes conduc tive and a 'voltage .drop appears across resistor .|16 which opposes the .bias impressed upon the .screen v.grid of the thyratron by the battery |14,

thereby lowering -theexciting voltage .of .tube |23 to that corresponding tozthe incoming pulse.

The critical adjustment of the bias on ztwo grids of a thyratron tends considerably -to stabilize the minimum voltage at -which `the tube becomes conductive. Even more effective in this regard is the arrangement of Fig. 5, showing a modification .of .the portion of the .circuit of Fig. .4 which is between lines Zf-iZ and W-W. In this modiiication the resistor is replaced by `a vacuum tube `|82 having a variable .cathode .-resistor |83. The eiect of the arrangement iof Fig. 5 is that, as soon as the tube 1'11 lbecomes 4con ductive, the current through tube |82 will increase whereby, due to the cathode follower effect of resistor |83, the inner resistance of tube |82 will increase, thereby driving the screeny :grid of `tube |23 even more sharply .positive when a .pulse-Sullicient to render tube |11 conductive is received. The variability of resistor |=83 allows for the accurate adjustment of the bias of tubel |23.

It will be understood that the arrangement .of Fig. 4 or 5 may be applied not only to the thyratrons of Fig. 2'butalso to tube 42 of Fig. v1, if desired.

Although the invention ha'sbeen described with reference to the remote control .of -a radio `recel-ver, it by no means limited' to a .system of this character but may be adapted to a variety of purposes. An obvious field for its application is, for example, in combination with automatic telephone systems wherein the -control station represents a calling subscriber and the controlled station a central oflice having means for connecting the calling subscriber with a selected one of a plurality of other subscribers. Again, the subscriber may be a broadcast listener connected by way of a transmission line to a central station --12 receiving .a plurality of programs, transmission of a particular switching signal venabling such subscriber to be connected .to a speciiic one of the programs received at the central station.

Furthermore, it is :to be understood thatV the specic circuit elements disclosed, or their 'relative arrangement, may be -modiiied in various Ways without departing from Vthe. spirit or fexceeding the scope of the invention. It will -be possible, for example, to replace the two-wire vltransmission line herein referred to by a single ywire with 'ground return, by a coaxial cable, .or lby'any other transmission channel capable of transmitting D.C. voltages. What we claim-as novel, and desire to secure by Letters Patent, is;

'1. 'In a remote control system, in combination, a' conductive transmission channel, a source of D.C. potential at one end of said channel, means including-said source for applying a selected one .oiga plurality of predetermined D.C. voltages 'to said channel yfor transmission to the other end of said channel, a plurality of loads at said other rend, a plurality of selectively biased selector elements at said other end, means including said selector elements Afor connecting .a respective one of said loads to `saidvchannel as determined by the magnitude of the selected voltage, and a plurality of switching elements actuatable by the 'said yselector elements, respectively, and provided `with locking means, said locking means being 'interconnected so that only an end elementi-in la chain of actuated switching elements will remain actuated after the associated selector ele- ;ments havebecome inoperative.

'2. The combination according to claim 1, wherein-.each of said loads is connectable to said channel 'by means of a respective switching cirlcuit arranged to be completed when all but a -corresponding one of said switching elements areunactuated.

3. A `remote control system comprising a .con- 'trol station, a lremote station and a conductive lchannel interconnecting said stations; saidwcontrol station comprising a plurality of sources of different but xed potentials, and pulse generator means operable to connect a selected -source of potential to said channel whereby a D.C. voltage pulse of a magnitude corresponding to the potential of said selected source is transmitted to said remotestation; said remote station comprising a plurality of voltageresponsive elements, biasing means making each of said elements responsive to a respective minimum voltage only, said minimum voltages substantially corresponding to .said xed potentials, respectively, a plurality of switching elements each actuatable by a respec- 'tive voltage-responsive element when the latter responds, locking means interconnected so that only an end element in a chain of actuated switching elements will remain actuated after the response of the associated voltage-responsive elements has ceased, a plurality of loads, and a plurality of switching circuits each arranged to connect a respective load to said channel when all but a respective one of said switching elements are unactuated.

4. A system laccording to claim 3, wherein said channel is terminated at the remote station in an impedance which is high relative to the internal impedance of any of said potential sources.

5. A system according to claim 3, wherein said voltage-responsive elements are normally disconnected from said channel, and wherein an additional voltage-responsive element is provided responsive to any of said pulses and arranged -to connect all of said normally disconnected elements across said channel at the beginning of each pulse.

6. A remote control system comprising a control station, a remote station and a transmission line interconnecting said stations; said control station comprising a plurality of sources of diiierent but fixed potentials, a plurality of manually controllable switches, and pulse generator means operative upon actuation of any one of said switches to connect a respective one of said sources across said line for a predetermined period, whereby a D.C. voltage pulse of a magnitude corresponding to the potential of said respective source is transmitted to said remote station; said remote station comprising a plurality of normally non-conductive electronic devices, voltage-responsive means for connecting the inputs of said devices in parallel across said line, biasing means arranged to render each of said devices conductive upon .application thereto of a minimum voltage corresponding to the potential of a respective one of said sources, a plurality of relays each operable upon excitation of a respective one of said devices, said relays having armatures connected in circuit in the order of the magnitudes of the exciting voltages of the associated electronic devices, at least certain of said relays having front and back contacts, the connection of said armatures being such that a holding circuit is closed only for that one of a series of operated relays which is controlled by the electronic device having the highest exciting voltage, a plurality of loads, and circuit means including a front contact of the respective relay and back contacts of all other of said relays for respectively connecting each of said loads across said transmission line.

'7. A system according to claim 6, wherein said voltage-responsive means comprise an additional electronic device responsive to pulses derived from any of said sources, and a further relay operative upon excitation of said additional device.

8. A system according to claim 7, comprising yet another relay operative upon excitation of said additional device to open the holding circuit of any relay previously operated, and circuit means including said further relay for de-energizing said other relay shortly after the beginning of a pulse.

9. A system according to claim 6, wherein said pulse generator means include a set of control relays each energizable upon actuation of a respective one of said manually controllable switches, each of said control relays being provided witli a holding circuit including back contacts of all other control relays whereby only one control relay will remain energized subsequent to the actuation of said respective switch.

10. A system according to claim 9, wherein said pulse generator means further include a reactance in series with all of said holding circuits, and relay means operable in response to a current surge through said reactance to disconnect said respective source of potential from said line.

11. A system according to claim 6, further comprising an electronic device connected across said transmission line and responsive to voltages derived from any of said sources to disable all of said manually operable switches until the pulse applied to the line has decayed below a predetermined level.

12. A remote control system comprising a control station, a remote station and a transmission line interconnecting said stations; said control station comprising a source of positive potential, ai source of negative potential, a plurality of additional sources of iixed but different potentials of given polarity, rst switch means operable to connect one of the two first-mentioned sources across said line whereby an "On signal is sent to said remote station, second switch means operable to connect the other of the two first-mentioned sources across said line whereby an Ofi signal is sent to said remote station, and a plurality of third switch means each operable to connect a respective one of said additional sources across said line whereby a respective switching signal is sent to said remote station; said remote station comprising a plurality of loads, a plurality of electronic selector means each adapted to connect a respective one of said loads across said line in response to a respective one of said switching signals, a first electronic switch responsive to said On signal to connect power to said electronic selector means so as to place the same in condition to respond to said switching signals, and a second electronic switch responsive to said "05 signal to disconnect power from said electronic selector means.

1.3. A system according to claim l2, wherein said Off signal is of the same polarity as said switching signals.

14. A system according to claim 13, wherein said Off signal is of greater magnitude than any of said switching signals.

15. A system according to claim l2, wherein said switch means include a timer operable to send at least certain of said pulses over said line in a predetermined order.

16. In a control system, in combination, a gasfllled electron tube having a cathode, an anode and at least two grids, a source of control voltage connectable across said cathode and one of said grids, a biasing circuit for the other of said grids normally maintaining said other grid at a potential sufficiently negative to prevent application of said control voltage to said one grid from ionizing said tube, an electronic control device having an input circuit and an output circuit, an impedance common to said output and biasing circuits, and a connection for applying said control voltage to said input circuit so that a voltage drop sufficient to render said tube conductive will be developed across said impedance.

17. The combination according to claim 16, wherein said control Adevice is a vacuum tube biased to cutoll" in the absence of said control voltage.

18. The combination according to claim 16, wherein said common impedance is a cathode resistor of said control device.

19. The combination according to claim 18, wherein said biasing circuit comprises a resistor and a vacuum tube having at least three elements, said elements including an anode connected to said impedance, a cathode connected to said resistor and a grid connected to a. point of xed potential.

MICHEL N. YARDENY. ADOLPH RAZDOWITZ.

REFERENCES CITED The following references are of record in the le of this patent:

'UNITED STATES PATENTS Number Name Date 2,196,319 McLaughlin Apr. 9, 1940 2,305,862 Gilliver et al. Dec. 22, 1942 

